Incomplete Dominance vs. Codominance: Beyond Dominant and Recessive Problems (p 274)
Define Incomplete dominance.
5.
Chicken feathers exhibit Codominance.
 The allele B codes for Black feathers
 The allele W codes for White feathers.
GENOTYPES:
HH
Homozygous
for ability to make
LDL receptors
Hh
Heterozygous
hh
Homozygous
for inability to make
LDL receptors
6.
PHENOTYPES:
Cholesterol 2X
1/500 people
Cholesterol 5X
Heart attacks as
Early as 2 Yrs old!!!
1/million people
Liver cell w/
Half the receptors
Liver cell w/ OUT receptors
Normal liver cell
What would happen if a Black chicken
(BB) were crossed with a “Erminette” –
black and white speckled roster (BW)
A. Complete the Punnette
square 
B. What is the expected
genotype ratio
___BB: __BW: ___WW
Egg from Mother
C.
A couple who are expecting
their first baby. The woman’s
cholesterol is 2x normal levels
because she genotype is
Heterozygous (Hh). Her
husband has normal
cholesterol levels (HH)
A. Complete a punnett square.
B.
Possible
Genotypes
Of offspring
Horse Hair exhibits Codominance
 The allele R codes for Red hair
 The allele W codes for White hair
 A Roan colored horse has the genotype RW and will
The probability that the baby will have…
______ %.
 High cholesterol levels is _____%
 VERY high cholesterol levels is _____%
 Normal cholesterol levels is
produce both Red & White hairs
Egg from Mother
7.
3.
What would happen if two
Pink (RW) 4 O’clock
flowers were crossed?
A. Complete a Punnett square
Gametes from 2nd parent mentioned in word problem
4 O’clock flowers & Incomplete dominance
 The allele for
white is W.
 The allele for
Red is R.
What is the expected
phenotype ratio
Possi
Geno
Of off
___ Black: __: “Erminette”: ___ white.
Sperm from father
2.
Egg from Mother
Sperm from father
Incomplete dominance in human HYPERCHOLESTEROLEMIA

Receptors on liver cells take LDL cholesterol out of the blood
Define Codominance.
Gametes from 1st parent mentioned in word problem
A Roan colored female (RW) is
breed with a Roan colored male
(RW)
A. Complete the punnett Sq
B. The possibility that the
offspring will have…
______ %
 A Roan haired coat is ______ %
 A white haired coat is ______ %
 A Red haired coat is
Possible
Genotypes
Of offspring
Sperm from father
1.
Poss
Geno
Of of
Blood type Exhibits Codominance
 Blood type AB is the equal expression of the two alleles
IA and IB
 We will ignore blood type O until another lesson
8.
B.
What is the genotype ratio ___RR:
___ RW: ___WW
C.
What is the phenotype ratio ___Red:
D.
____________True/False: If you know the phenotype (physical
appearance), you do NOT know the genotype (2 letter combination).
__ Pink: ___white
What possible blood types could a baby have, if both parents have blood
type AB (genotype I
A
B
and I )
Egg from Mother
IA
IB
IA IA
IA I B
CC – genotype
CS - genotype
SS – genotype
Curly- phenotype Wavy – phenotype Straight - phenotype
4.
Sperm from father
Human Hair:
C = Curly alleles S = Straight allele
A woman with naturally curly hair is pregnant. The baby’s father has
wavy hair.
A. Complete a Punnett Square
B. What is the genotype ratio ___CC: ___ CS: ___SS
C.
What is the phenotype ratio ___Curly:
__ Wavy: ___ straight
Sperm from father
Egg from Mother
IA
Possible
Genotypes
Of offspring
Possible
Genotypes
Of offspring
IB
IA IB
IB I B
A.
The baby’s would have a ______% of having blood type A
B.
The baby would have a ______% chance of having blood type B
C.
The baby would have a ______% chance of having blood type AB